1. Technical Field
The disclosure relates to a joining structure for joining tubes made of different kinds of metal or alloy. The disclosure also relates to a biopsy needle to which the joining structure is applied.
2. Related Art
There is known a biopsy needle as a treatment tool for collecting a cell or tissue in a living body. The biopsy needle has a cylindrical shape having a hollow space and collects a cell or tissue by puncturing a living body with the distal end portion thereof. There is also known a biopsy needle used as a treatment tool in an endoscope system which observes the inside of the lumen of a living body. Such a biopsy needle is inserted into the lumen through a treatment tool channel which is formed in an insertion unit of an endoscope to collect a cell or tissue of the wall surface.
The biopsy needle used in the endoscope system has a substantially linear shape, and includes a tubular needle which has a distal end portion capable of puncturing a living body, a needle tube which extends from the needle, and a tubular member into which the needle and the needle tube is insertable. In a conventional biopsy needle, the needle and the needle tube are integrally formed of, for example, stainless steel (SUS).
On the other hand, in recent years, a biopsy needle that includes a needle formed of a nickel-titanium (NiTi) alloy has also been put to practical use. A nickel-titanium alloy has an extremely high elastic function which is also called a superelastic function. Thus, a nickel-titanium alloy is flexibly deformed in response to an external force and substantially completely restored when the external force is eliminated. Thus, when a needle is formed of a nickel-titanium alloy, it is possible to easily move the needle forward and backward even with respect to a passage which is curved in a complicated manner.
If a needle and a needle tube are formed of different materials, there is known a technique in which the needle and the needle tube are inserted into a sleeve-shaped coupling member which is made of, for example, stainless steel (SUS), causes the distal end faces of the needle and the needle tube to abut on each other, and joins the needle, the needle tube, and the coupling member to one another with a brazing material or an adhesive (refer to WO 2006/065913 A, for example).